libpthread_dbg(3) is a remnant library from the M:N thread model
(pre-NetBSD-5.0) API to introspect threads within a process and for use
of debuggers.
Currently in the 1:1 model it's not used in GDB neither in LLDB and it's
not either planned to be used. It's current function to read pthread_t
structures is realizable within a regular debugger capable to
instrospect objects within a tracee (GDB, LLDB...).
pthread_dbg(3) is going to be removed from the base distribution and moved
to pkgsrc.
Patch reviewed by <christos>
Sponsored by <The NetBSD Foundation>